docs: def _handle_relation_harness(self, line: str, position: int, tokens: Union[ParseResults, Dict]) -> ParseResults:
          """Handle BEL relations based on the policy specified on instantiation.
  
          Note: this can't be changed after instantiation!
          """
          if not self.control_parser.citation:
              raise MissingCitationException(self.get_line_number(), line, position)
  
          if not self.control_parser.evidence:
              raise MissingSupportWarning(self.get_line_number(), line, position)
  
          missing_required_annotations = self.control_parser.get_missing_required_annotations()
          if missing_required_annotations:
              raise MissingAnnotationWarning(self.get_line_number(), line, position, missing_required_annotations)
  
          self._handle_relation(tokens)
          return tokens